Ship bottoms, underwater structures, fishing nets and the like, when exposed to water for a prolonged period of time, are likely to have their appearance and functions damaged by the attachment to surface and propagation thereon of various aquatic organisms including animals such as oysters, mussels and barnacles, plants such as seaweeds (laver) and bacteria.
In particular, when such an aquatic organism attaches to a ship's bottom and propagates thereon, it may occur that the surface roughness of the ship as a whole is increased to thereby lower the speed of the ship and increase the fuel consumed by the ship. Removing of the aquatic organism from the ship bottom necessitates spending of extensive labor and working time. Also, when bacteria attach to, for example, an underwater structure and propagate thereon and, further, slime (sludgy matter) attaches thereto to cause putrefaction, or when a large sticky organism attaches to the surface of an underwater structure, for-example, steel structure and propagates thereon-to thereby damage the coating for corrosion prevention provided on the underwater structure, there is the danger that damages such as deterioration of the strength and functions of the underwater structure and thus marked shortening of the life thereof are invited.
For preventing such damages, it is common practice to apply various antifouling paints to ship bottoms, etc. For example, the following antifouling paints have been proposed.
(1) Japanese Patent Laid-open Publication No. 63(1988)-128084 discloses an antifouling paint comprising as a vehicle a metal-containing resin composition obtained by heating a base resin containing an acid group, a metal salt of low-boiling-point organic basic acid (provided that the metal is a bivalent or higher valence metal having lower ionization tendency than those of alkali metals) and a high-boiling-point monobasic acid while removing low-boiling-point organic basic acids from the system so as to effect reaction thereof.
In Example 42 of this publication, there is disclosed an anti-fouling paint comprising a varnish of naphthenatocopper (meth)acrylate/MMA/2-ethylhexyl acrylate copolymer mixed with a tetraphenylborane pyridinium complex. Further, in Example 43 of this publication, there is disclosed an antifouling paint comprising a varnish of oleatozinc (meth)acrylate/MMA/ethyl acrylate copolymer mixed with cuprous oxide.
(2) The present applicant in Japanese Patent Laid-open Publication No. 11(1999)-323209 proposed an antifouling coating composition comprising (a) a (meth)acrylic acid metal salt based copolymer and (b) a pyridine triphenylboron or triphenylboron amine complex of the formula:

(in the formula, R is H, an alkyl having 3 to 30 carbon atoms, a substituted or unsubstituted pyridyl or a substituted or unsubstituted aromatic group).
(3) Furthermore, an antifouling paint comprising a complex, the complex composed of triphenylborane and an amine having 6 or more carbon atoms, and a hydrolyzable resin is disclosed, and as the hydrolyzable resin, there is mentioned a resin comprising a (meth)acrylic resin having at side chain ends thereof the formula: (CH2)m.COO.M.Ln (wherein m: integer of 0 to 2, n: atomic valence of metal −1, M: Zn, Cu, etc. and L: alkyl, carboxyl, etc.) (see Japanese Patent Laid-open Publication No. 11(1999)-302572).
However, all the antifouling coating compositions described in the above publications (1) to (3) contain antifoulants, such as cuprous oxide, causing relatively heavy burdens on the environment. Accordingly, there has been room for further improvement to the obtained coating films from the viewpoint of, for example, reducing burdens on the environment.
Moreover, Japanese Patent Laid-open Publication No. 11(1999)-35877 and Japanese Patent Laid-open Publication No. 2002-12630 describe antifouling paints comprising metal-containing resin compositions. However, the development of antifouling paints of further enhanced performance has been demanded.
As apparent from the above, there is a demand for the development of an antifouling coating composition capable of forming a superior antifouling coating film which is wasted at constant rate irrespective of the coating location for a prolonged period of time and which can maintain excellent antifouling performance for a prolonged period of time, being applicable to ocean-going vessels.
In this situation, the inventor has conducted extensive and intensive studies. As a result, it has been found that the use of specified copolymer (A) containing a metal as a resin component and the simultaneous use of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (B) combined with a metal pyrithione compound (C) as an antifoulant enable realizing excellent antifouling performance even without the use of cuprous oxide and an organotin. It has further been found that the coating film from the obtained antifouling coating composition exhibits various advantageous characteristics, such as reducing of burdens on the environment, wasting of coating film at constant rate irrespective of the coating location for a prolonged period of time, maintaining of excellent antifouling performance for a prolonged period of time, being applicable to ocean-going vessels, resistance to cracking and peeling, increased adhesion as compared with that of a coating film based on pyridine-triphenylborane, etc., sharp hue and reducing of discoloration after water immersion or exposure. The present invention has been completed on the basis of these findings.
The present invention has been made with a view toward solving the above problems of the prior art. It is an object of the present invention to provide an antifouling coating composition from which an excellent antifouling coating film, which can reduce burdens on the environment, realizing uniform wasting of coating film at a constant rate for a prolonged period of time (uniform wasting performance of coating film) and which can maintain excellent antifouling performance for a prolonged period of time (long-term antifouling performance maintaining capability), being applicable to even ocean-going vessels, can be formed. It is other objects of the present invention to provide such an antifouling coating film and, covered with the antifouling coating film, a marine vessel, underwater structure and fishing gear or fishing net and to provide a method of fouling prevention therewith.